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UPEEC

Active Filters

Op-amps with RC networks make filters with gain, sharp roll-off and no inductors.

Intermediate
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The Sallen–Key topology builds a second-order (−40 dB/decade) low- or high-pass filter with one op-amp. For equal components:

fc=12πRCf_c = \frac{1}{2\pi RC}

Response shapes:

  • Butterworth — maximally flat passband (Q=0.707Q = 0.707).
  • Chebyshev — steeper roll-off, ripple in the passband.
  • Bessel — best step response, linear phase.

Stack stages for higher order. Free tools (TI Filter Designer, Analog Devices Filter Wizard) compute the values.

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